Chest pain is a very common and a complex symptom that medical practitioners need to accurately diagnose on a daily basis. The diagnosis for patients with chest pain range from myocardial spasms to acute myocardial infarction (AMI). An accurate and correct diagnosis saves lives while misdiagnosis may lead to serious morbidity and mortality to the patient. Medical practitioners rely on their experience and diagnostic tools such as, for example, electrocardiography (ECG), serum markers, ionizing radiation, dobutamine stress echocardiography (DSE), single photon emission computed tomography (SPECT), positron emission tomography (PET) and magnetic resonance imaging (MRI) to furnish a diagnosis on a patient's condition. Unfortunately, medical practitioners invariably face the risk of malpractice actions being started against them subsequent to their failure to diagnose a patient correctly. This is disturbing for the medical practitioners, especially when their diagnostic tools are constrained in their capabilities.
There are currently limitations in relation to the use of serum markers. The more notable limitations relate to: (i) no single determination of one serum biochemical marker of myocardial necrosis reliably identifies or reliably excludes AMI less than six hours of symptom onset; (ii) no serum biochemical marker identifies or excludes unstable angina at any time after symptom onset; and (iii) the lack of diagnostic sensitivity of point-of-care devices resulting in the overlooking of elevations of cardiac troponin levels.
Similarly, there are also limitations in relation to the use of twelve lead ECGs. These limitations include: deciphering atypical electrocardiograms of patients with AMIs, inaccurate static analysis of a dynamic process like AMI, and the fact that electrocardiograms are more like prognostic (predictive) tools rather than diagnostic tools.
There is currently no known disclosure of the use of ECGs to quantify the mass of viable myocardium in the heart. Current methods of quantifying viable myocardium are not ideal. Techniques, such as, for example, SPECT, DSE, and PET, are unable to measure the direct presence and exact quantity of viable myocytes. In SPECT and PET, inaccuracies arise due to poor spatial resolution. Likewise, in DSE, inaccuracies arise because of errors in registration between comparison images, and an inability to visualize all parts of the left ventricular myocardium. At the present moment, an MRI may be used for the determination of infarct size, assessment of myocardial viability and assessment of myocardial ischaemia. However, MRI costs are still rather prohibitive, consequently restricting their availability to well funded medical institutions.
It is well-known that although most akinetic segments of ventricular myocardium correspond to infarcted regions, a variable amount of myocytes survive the acute ischaemic insult and remain at risk as critical narrowing or occlusion of the infarct vessel, in most cases, persists without intervention. The survivability of myocardium depends on residual perfusion, energy demands, and the metabolic and hormonal environment, among other factors. Detecting viable myocardium is of significant clinical relevance for a number of reasons. Firstly, a region may recover contractile function, at least to some extent, and thereby not only improve symptoms of heart failure, but also reduce morbidity and mortality. Secondly, viable myocardium in a critically perfused region may represent a substrate for life-threatening arrhythmia. Thirdly, residual viability in akinetic regions tends to disappear gradually, even without recurrence of an acute coronary event (this is significant as operative mortality in coronary patients with poor ventricular function is lower in the presence of viable myocardium, and timely intervention may further reduce the risk). Finally, preservation of even a small layer of viable myocardium in an infarcted region may prevent progressive remodeling and failure. Thus, assessment of tissue viability allows for better stratification of coronary patients with compromised left ventricular function, and improves the selection of high-risk patients for invasive procedures.